Near infrared spectroscopy-measured changes in cerebral blood volume and cytochrome aa(3) in newborn lambs exposed to hypoxia and hypercapnia, and ischemia: a comparison with changes in brain perfusion and O-2 metabolism

Objectives: Validation of near infrared spectroscopy (NIRS)-measured change s in cerebral blood volume (Delta CBV) and cytochrome aa(3) (Delta Cytaa(3) ) as estimators of changes in brain perfusion and oxygenation in the newbor n lamb during hypoxia and hypercarbia, and additional hypotension. Methods and materials: In 33 newborn lambs brain perfusion assessed by carotid arte ry blood flow (Delta Q(car): ml/min)and cerebral metabolic rate of oxygen ( Delta CMRO2: ml O-2/min) were related to NIRS-derived Delta CBV (ml/100 g) and Delta Cytaa(3) (mu M) during combined hypoxia and hypercarbia and addit ional hypotension. Combined hypoxia and hypercapnia was induced by ventilat ion with 6-8% of O-2 and 10% of CO2 during 30 min, and additional hypotensi on (< 35 mmHg for 5 min) was induced by careful withdrawal of blood. Result s: CBV increased during hypoxia and hypercarbia, decreased during additiona l hypotension and was related to Delta Q(car): (0.009 ml/100 g change per m l/min Q(car): P < 0.0001). Cytaa(3) increased during hypoxia and hypercarbi a, decreased during subsequent additional hypotension and showed a reverse relationship with Delta CMRO2 (-1.65 mu M change per ml O-2/min CMRO2: P < 0.0001). Cytaa(3) remained above baseline during reperfusion. Conclusions. Delta CBV estimates changes in brain, perfusion, but overestimates brain pe rfusion during hypotension. The pattern of Delta Cytaa(3) suggests less oxy gen utilisation by brain tissue during hypoxia and subsequent reperfusion. (C) 1999 Elsevier Science Ireland Ltd. All. rights reserved.